1. Field of the Invention
The present invention relates to a control technique for a data storage system comprising two or more separately established host devices.
Furthermore, the present invention relates to an exclusive control technique for duplicated volumes generated between two separately established storage devices having a remote copy function.
2. Description of the Related Art
The various IT technologies for sustaining 24-hour service without a system stoppage are of particular interest to companies promoting e-business development. One of those is clustering, a technology for realizing high availability. This technology is used mainly for systems performing database operations, wherein systems of multiple devices are combined and constructed so that the entire system can work without stopping even when part of the system fails. For example, a small scale system has a constitution using a single shared disk among a plurality of servers and a SCSI interface is used between the servers and the shared disk. If data handled by the plurality of servers is placed on the shared disk in this constitution, another server takes over the data on the shared disk and can continue processing if one server goes down. This is called a fail-over In a clustering system carrying out a fail-over in this way, operations are carried out so that a client can continue to use a single server.
In order for uniform determination of the host devices for performing fail-over in the clustering system, MSCS (Microsoft cluster server), a clustering product from Microsoft, has a single determining volume, called a quorum resource, for controlling the cluster configuration information.
There is exclusive control of this determining volume and this avoids the problem losing data integrity because of redundant possible error in source processing of a plurality of different processes at the same time on a single resource.
Next is explained a clustering system in the case of two or more host devices and two storage devices connected by a SCSI interface. In the clustering system, the host devices are each connected with a network interface. The host devices monitor each other""s operating status by sending messages to each other and performing heartbeat communications.
Furthermore, the clustering system detects when a failure occurs in a host device or in the network interface and heartbeat communications become impossible, and determines whether to continue with resources, applications, and services on another host device. A single determining volume for managing the clustering system is established in the storage devices as the sole element for making that determination.
Generally, in systems using a SCSI interface, one of a plurality of hosts has exclusive control (exclusive use) of a single target (for example, a magnetic disk drive). In such cases, it is possible to reserve a target and have the exclusive use thereof by initially issuing a SCSI reserve command.
In the case where a failure occurs in the host device or in the network interface and heartbeat communications become impossible, each of the host devices, in order to acquire exclusive usage rights in the clustering system, issues a SCSI reserve command to the determining volume and attempts to acquire exclusive usage rights. The host device whose SCSI reserve command to the determining volume was successful takes over all applications and services of other host devices and resources such as disk volumes and executes a fail-over. Meanwhile, the host devices whose SCSI reserve commands to the determining volume failed halt applications and services being performed thereon.
In this way, the clustering system realizes a state where one host device has exclusive use of the determining volume for managing the clustering system.
Clustering systems have become necessary, particularly in large-scale on-line transaction systems wherein large amounts of data must be processed in real time. These clustering systems support fail-over functions, wherein multiple servers, as well as disk devices and power sources, are provided and even if one fails, another takes over the processing in order that the system not be halted.
With the prior art, the determining volume in the clustering system is constituted by a single disk volume which can be accessed by all host devices.
However, in the clustering systems including a plurality of separately established host devices, the problems of establishing a single determining volume which all host devices can access include the case where the system cannot be constructed due to limits to the distance over which a connection can be formed with the cable for an interface, for example, a SCSI interface etc. of connection between the host devices and the storage device containing the determining volume.
Using a remote copy function, which can construct a disaster backup system and a system for data communications with remote sites, in a clustering system is considered as a means for resolving this.
The remote copy function realizes remote copying between storage devices without passing through host devices (host free). It is possible to ensure the logical integrity of data copied to the remote site in order to protect sequences for reflecting data updates to the remote site. Here, a method is considered wherein paired volumes (called the primary volume and secondary volume; there are a storage device containing the primary volume and a storage device containing the secondary volume) duplicated among separately established storage devices using the remote copy function are generated and, because it is ensured that the primary volume and secondary volume of the pair volume contain the same data, one of the host devices has exclusive use of either the primary volume or secondary volume as the determining volume.
Because each of the separately established systems is a system using a SCSI interface, each of the host devices can have exclusive control of the volume therein and there are two host devices, wherein one host device has exclusive use of the primary volume and one host device has exclusive use of the secondary volume.
Namely, in order to use the primary volume or the secondary volume exclusively, only issuing the SCSI reserve command can not perform an exclusive use of the determining volume because both volumes can be reserved respectively.
As discussed above, in the case of establishing a determining volume using a remote copy function, the primary volume and secondary volume forming the pair are recognized as separate volumes by each host device. In the case where each of the host devices issues a SCSI reserve command to the primary volume and secondary volume, the primary volume and secondary volume can be individually reserved. As a result, a plurality of host devices may operate the same applications and services at the same time and therefore serve not to function as a clustering system.
Consequently, it is an object that paired volumes generated among two storage devices having remote copy functions be recognized as a single determining volume for a clustering system comprising a plurality of host devices, and to realize a method for exclusively determining the host device which can issue update requests to the pertinent paired volumes from among a plurality of host devices in the clustering system. A technique is therefore proposed for the present invention wherein paired volume control software which operates the xe2x80x9cstatexe2x80x9d (attributes) of the paired volumes receives reserve commands which are SCSI commands issued from the clustering software on the host devices, the paired volume control software combines the paired volume control commands issued and issues those commands to the storage devices, and the response of the storage devices to those commands is to end normally only the host device which issued the reserve command first, and thereby enable uniform determination of the host device with exclusive use of the paired volumes.